Recently, batteries having a light weight, a long service life and a high energy density are demanded as a main power source or an auxiliary power source for electric automobiles and fuel cell vehicles, or as a power source for small-size electronics devices. For this demand, a non-aqueous electrolyte battery using lithium as an active substance for a negative electrode is known as one of the batteries having a high energy density because an electrode potential of lithium is lowest among metals and an electric capacity per unit volume is large, and many kinds of such a battery are actively studied irrespectively of primary battery and secondary battery, and a part thereof is practiced and supplied to markets. For example, the non-aqueous electrolyte primary batteries are used as a power source for cameras, electronic watches and various memory backups. Also, the non-aqueous electrolyte secondary batteries are used as a driving power source for note-type personal computers, mobile phones and the like, and further they are investigated to use as the main power source or the auxiliary power source for the electric automobiles and the fuel cell vehicles.
In these non-aqueous electrolyte batteries, since lithium as an active substance for a negative electrode violently reacts with a compound having an active proton such as water, alcohol or the like, the electrolyte used in these batteries is limited to an aprotic organic solvent such as ester compound, ether compound or the like.
Although the aprotic organic solvent is low in the reactivity with lithium as the active substance for the negative electrode, there is a high risk that if a large current flows violently, for example, in the short-circuiting or the like to cause the abnormal heat generation in the battery, the aprotic organic solvent is vaporized and decomposed to generate a gas, or the generated gas and heat cause explosion and ignition of the battery, or fire is caught by a spark generated in the short-circuiting or the like.
As to such a problem, there is studied a method for rendering the non-aqueous electrolyte for the battery flame retardant. For example, there are reported a method of using phosphates such as trimethyl phosphate or the like as an electrolyte and a method of adding a phosphate to the aprotic organic solvent (see JP-A-H04-184870, JP-A-H08-22839, JP-A-2001-182669 and the like). However, these usual triesters of phosphoric acid do not have sufficient non-combustibility, and are gradually and reductively decomposed on the negative electrode by repeating discharge-recharges, so that there is a problem that performances of the battery such as a cycle performance and so on are highly deteriorated.